I have both and they are best for different locations.
BL2000 in the kitchen and in the laundry room. No cloth that could be affected by moisture. The sound is perfect for smaller rooms. Very good speaker for listening on radio. No need for a remote. The buttons I use is mostly [stand by] to get the sound from the master room and of course the volume wheel.
BL3500 in the master bedroom. Black and elagant up on the wall with a clock as a bonus. Good speaker for music. No need for buttons as we use a remote anyway. I don't have a dining room, but if I would there would be a graceful BL3500 on the wall.
As a die hard "No visible cables!" the BL3500 has the advantage that the cables can totally be hidden (right into the wall with them). On the BL2000 this is not possible due to the locations of the sockets.
Beovision LX5500, BeoCord V6000, BeoSound 9000, BeoLab 8000, BeoLab 3500, BeoLab 2000, BeoVox1, BeoCom 6000, Form1, LightControl 1